Alloy



Patented Nov. 8, 1938 v PATENT OFFICE f 1 ALLOY Anthony G. de Goly er, New York, N. Y.

No. Drawing. Application December 4, 1936,

. Serial No. 114,205

2 Gla ims. (Cl. 75-126) 1 The present invention relates to a ferrous base alloy containing tungsten and boron. as well as certain other alloy elements.

The object of the present invention is to Pro- 5 vide an alloy which is entirely or substantially free from carbon and which has a combination of advantageous P ical properties and characteristics rendering it particularly valuable for L use as metal cutting tools.

The type of alloy tool steel usually classified as high speed" which has heretofore been in general usecontains tungsten as the principal alloy element; the standard 18-4-1 high speed steel being substantially an alloy of iron with 18% tungsten, 4% chromium, 1% vanadium, 0.50% to 0.75% carbon and minor percentages of manganese and silicon. Various modifications have been proposed, such as steels contain both tungsten and molybdenum in varying ratios; 1 1

All of the previously known high speed steels containing tungsten or molybdenum as the principal alloy element depend upon the presence of an appreciable amount of carbon to develop the degree 'of hardness necessary for metal cutting tools. An examination of any of the previj'ously known high speed steels discloses grains or particles of an excess constituent comprising" a complex compound of carbon, tungsten and. iron,-or carbon, molybdenum and iron as the case may be. This constituent is commonly'designated as the carbide segregate.

It is well vlrnow'n that a minimum carbon content of 0.50%;is necessary for the development of the requisite hardness and cutting efficiency in;high speed steel; the usual carbon content c of such steel being from 0.60% to 0.70%.

I have discovered that by combining appreciable amounts of tungsten, boron, chromium and 40 vanadium in a ferrous alloy entirely free from 7 carbon thatI can. produce a composition which a cutting efllciency superior to previously known high speed steels containing appreciable percentages 'of carbon. Furthermore, by'reason thermal treatment which is markedly different from that required'for heretofore known tool steels. By means of such thermal treatment of the freedom from carbon the alloy of the present invention isamenable to a method of con are usually present in minor amounts. Likewise phosphorus and sulphur, as well as certain other elements commonly found in alloy steels, are usually present in ineffective amounts in the nature of incidental impurities. 5

The alloy of the present invention comprises tungsten 9% to boron 0.25% to 2.15%, chromium 1% to 5%, vanadium 0.50% to 4% and the remainder principally iron. Manganese and silicon will usually be present in amounts not exceeding approximately manganese 1% and silicon 1.20%.

I prefer to have the alloy entirely free from carbon as when this element is absent the composition is not only more amenable to thermal treatment but, in general, has greater cutting efliclency. However,- byreason of the fact that certain of the .materials used in the preparation of the alloy frequently contain varying amounts of carbon I have found that when my alloy is 26 manufactured under ordinary commercial conditions it will frequently contain from about 0.03%- to 0.06% carbon in the nature of an incidental impurity. I have found that such incidental carbon can be present in-an amount as. high as approximately 0.10% without materially decreasing the valuable physical characteristics possessed by the carbon free alloy.

The presence of 0.45% or more carbon in high speed steels containing tungsten as the principal alloy element results in the formation of the carbide constituent or segregate referred to hereinabove. A relatively large portion of such constituent occurring in cast ingots is in comparatively massive form which can be reduced in size and; distributed throughout the steel only by mechanical working. It is well known that only the smallest particles of such carbide constituent can'be dissolvedin the matrix bymeans of heating. Consequently, a relatively large proportion of the primary carbide constituent persists through all of the thermal treatments to which such steels are subjected. Therefore, the regulation of particle size and distribution of a major portion of the complex tungsten carbide constit- 46 uent forming the segregate is entirely dependent upon mechanical working. This does not provide a satisfactory method of control of the physical structure of the aggregate.

It has previously been proposed to employ 50 boron as an essential component in high speed steels containing from 0.30% to 0.80% carbon.

I have discovered that when effective amounts of boron, i. e. 0.15% and higher are introduced into such steels that the segregate comprises a com plex compound containing boron, carbon, tungsten aid iron. I have found that such boro-carbide compounds are extremely hard and brittle and that relatively coarse particles of'this constituent cannot be appreciably fragmented by mechanical working without rupturing the steel. I have also discovered that such boro-carbide constituents are only partially dissolved in the matrix by thermal treatment. It will be evident, therefore, that the presence'of an appreciable percentage of such complex boro-carbides produces a steel in which the particle size and dissemination of the hard constituent cannot be closely regulated by thermal treatment.

' In the alloy of the present invention the segregate of the cast structure appears to be essensical properties and characteristics of the alloy can be accurately controlled by means of suitable thermal treatment. As an illustration one satisfactory method consists essentially of heating an aggregate of the alloy to a temperature in excess of 1000 C.; maintaining the aggregate at such temperature for a sufficient period of time to dissolve an appreciable proportion of the tungstenboron-iron segregate in the matrix; quenching the aggregate to substantially retain the solid solution; subsequently heating the aggregate to a temperature substantially lower than that at which the solid solution was formed for a suflicient period of time to produce precipitation of tungsten-iron-boride particles from the solid soluti on. I have found that in carrying out the primary heating for efiecting solid solution it is not necessary to dissolve all ofthe tungsteniron-boride constituent in the matrix. After the alloy has been quenched from the primary heating temperature it will usually have a hardness of approximately 48'to 52 Rockwell C compared to a hardness of from 62 to '70 Rockwell C which can be developed by precipitation of the tungstenboron containing constituent during the secondary heating. It will be apparent that by regulating the temperatures and periods of heating the ratio of precipitated boron compound to matrix constituent, or to primary boron compound may be accurately controlled. The precipitated boron compound is uniformly disseminated throughout the aggregate. 1

I have found that the boron containing constituent of the present alloy is not only extremely. hard but is relativelystrong. The presence of boron imparts high impact strength to the alloy,

particularly at temperatures generated'in the tip of a metal cutting tool. Such boron containing compounds are also highly resistant to oxide.-

tion at such temperatures, and consequently the injurious efiect of decarburization, which occurs in carbon containing tools, is entirely eliminated. Although thegreatest scope of usefulness of this alloy appears to be in cast or wrought forms as cutting tools, I have found it may be used for many other industrial applications such as forming dies, wearing parts, etc. v Iclaim: v 1. An alloy containing tungsten 9% to 20%, boron 0.25% to 2.15%, chromium 1% to 5%, vanadium 0.50% to 4%, manganese not exceeding approximately 1%, silicon not exceeding approximately 1.20% and the remainder iron.

2. An.alloy containing tungsten 9% to 20%, boron. 0.25% to 2.15%, chromium 1% to 5%, vanadium 0.50% to 4%, manganese not exceeding approximately 1%, silicon not exceeding approximately 1.20%, carbon not exceeding approximately 0.10% and the remainder iron.

ANTHONY G. on GOLYER. 

